Technical Field
The present invention relates to an ink composition, an ink cartridge, an ink jet recording device, and recorded matter.
Background Art
Inkjet printers have been drastically diffusing because of their advantages such as low acoustic noises and low running costs and printers capable of printing color images on plain paper are introduced into the market actively. However, it is extremely difficult to satisfy all the properties required of images such as color reproducibility, abrasion resistance, durability, light resistance (fastness), drying property, feathering, color bleed, duplex printing, and ink discharging stability. As a result, the ink used is selected based on the prioritized particular application.
In general, the ink for use in inkjet printers is mainly composed of water, with a coloring agent (colorant) and a hydrosoluble solvent such as glycerin to prevent clogging, etc. As the colorant, dyes are widely used for their excellent coloring and stability. However, the light resistance and water resistance of images of dyes are insufficient. Water resistance is improved to some degree by using special recording media for inkjet having an ink absorbing layer, but is not satisfactory when it comes to plain paper.
To compensate for such defects, ink using a pigment has begun to be used as a colorant. Although pigment ink is successful and superior to dye ink with regard to light resistance, water resistance, etc., the coloring of pigment ink is degraded by coherence of beams of light having different wavelengths and phases produced by multiple reflections of the beams of light within the pigment. For this reason, pigment ink is considered to be inferior to dye ink in general with regard to coloring.
In an attempt to compensate for such degradation of coloring of pigment ink, pigment particulates that are coated with resin are used. According to this method, the fixing property and the gas resistance property of the pigment ink are further improved by a resin, and in addition dispersion is greatly stabilized. However, currently, pigment ink is not still on a par with dye ink with regard to gloss.
In addition, high performance is demanded upon increasing demand in industry. As printing performance is improved, inkjet printers having line heads are proposed. In attempts to improve the performance, a device for quick drying by adding a permeating agent to an ink to permeate water into a recording medium is proposed to speed up drying of the ink attached to a recording medium.
However, the permeating property of the pigment is also improved in addition to that of water, thereby degrading image density. In addition, discharging stability is not satisfactory so that further improvement is desired.
Moreover, plain paper involves problems when it is used as a recording medium such that the surface of the plain paper swells by water serving as the solvent of an ink immediately after printing, which causes the difference of elongation ratio between both surfaces of the plain paper wider, resulting in occurrence of curling. This kind of phenomenon is not a problem for printing at low speeds since it is canceled as drying proceeds. However, as the printing speed increases, recording media are transferred before curling is canceled, which naturally results in paper jam. Increasing the content of an organic solvent in an ink suffices for curling. However, the hydhydrophobicity of the ink becomes strong, which makes it difficult to secure storage stability.
In view of the foregoing, ink compositions are demanded that improve coloring, which is an issue for conventional pigment inks, and have excellent storage stability and discharging stability.